- Material Selection: Building a Dual Foundation of Flexibility and Functionality
Material selection is the core of micro–nano stickers used in wearable devices. The materials must simultaneously provide flexibility, biocompatibility, and functional specificity—solving the conflict between “rigid functions” and “flexible substrates.”
The substrate layer, which directly contacts the skin, requires ultra-thinness, high elasticity, and breathability to achieve ergonomic, skin-friendly, and form-fitting performance. Silicone-based materials such as PDMS and Ecoflex, with elongation rates exceeding 100% and excellent biocompatibility, are ideal for skin-mounted electrodes and sensing layers. Electrospun nanofiber membranes, with a thickness of only 1–10 μm and high porosity, maintain long-term breathability and prevent discomfort from heat and moisture buildup—highly suitable for wearable applications.
The conductive layer must balance conductivity with stretchability. Silver nanowires and gold nanowires offer conductivities of 10⁶–10⁷ S/m and can be printed onto flexible substrates, withstanding 10–20% tensile deformation—ideal for primary circuits and electrodes. Graphene and carbon nanotubes have slightly lower conductivity but excellent stretchability (over 50%), and can form high-sensitivity strain sensors using nano-imprinting. Liquid metals, such as gallium–indium alloys, provide “infinite stretchability” when encapsulated in microchannels, making them suitable for joints or areas with large deformation.
Functional layers can be customized based on application needs: VO₂ for thermal sensing, enzyme-functionalized nanomaterials for biochemical monitoring, drug-loaded microneedle arrays for therapeutic purposes, or PVDF piezoelectric films for energy harvesting—realizing the concept of “material equals function.”
- Structural Design: A Multi-Layered, Skin-Inspired System
Micro–nano stickers adopt a multilayer collaborative architecture that mimics the layered structure of human skin, ensuring independent functionality while enabling interlayer synergy.
The adhesive layer uses medical-grade acrylic pressure-sensitive adhesives (5–20 μm thick) with shear strength above 500 kPa, ensuring secure adhesion during movement and residue-free removal.
The core functional layer integrates sensing, circuits, energy, and communication:
Sensing arrays include micro-scale temperature and bioelectrical sensors (10–50 μm thick).
Conductive circuits fabricated via nano-imprinting use silver-nanowire traces under 5 μm thick; serpentine patterns allow over 200% stretch without failure.
The energy layer employs ultra-thin solid-state batteries or triboelectric nanogenerators (20–100 μm), supporting 8–72 hours of operation.
Communication modules integrate flexible NFC chips and spiral antennas, maintaining over 90% signal strength during bending.
Structural innovations solve adhesion and deformation challenges:
Pyramid-shaped micro-nano protrusions (50–500 μm) increase skin contact area and triple adhesion strength.
Gradient-stiffness interfaces prevent stress concentration between layers.
Embedded microfluidic channels (50–200 μm) enable sweat sampling and heat dissipation.
The top protective layer uses 5–10 μm PTFE coating with IPX6 water resistance and UV protection, while maintaining >3000 g/m²/24h oxygen transmission for balanced durability and breathability.
- Functional Integration: From Monitoring to Interactive Intelligence
Function integration centers on “precise sensing + intuitive interaction,” with miniaturization and multimodal fusion as key directions.
Sensors manufactured via micro–nano fabrication achieve millimeter-level size and micrometer-level precision.
Pulse-wave electrodes achieve signal-to-noise ratios >40 dB.
Strain sensors respond within 0.002 s and detect up to 17 gesture patterns.
Multimodal systems integrate physiological monitoring (ECG, EMG), environmental sensing (UV, PM2.5), and motion tracking, enabling comprehensive health management.
Circuit integration combines nano-imprinting and direct-write printing with 10 nm resolution—reducing costs by 70% compared to photolithography—and allows circuits to be formed directly on curved surfaces such as wrists and joints.
Scenario-specific designs enhance precision:
Medical monitoring patches: nanoporous gold electrodes (contact impedance <1 kΩ), 60% reduction in motion artifacts; microneedles painless sample interstitial fluid for glucose measurement in 5 minutes.
Sports patches: microchannel networks for accelerated sweat removal; overall weight <1 g for zero-burden performance.
Interactive display patches: integrated MicroLED arrays and piezoelectric haptics show data and provide silent vibration alerts; EMG and pressure signals enable “thought + touch” dual-mode interaction.
- Performance Optimization & Manufacturing Scalability
Performance optimization addresses user pain points:
Bio-mimetic mushroom-head microstructures enable stronger adhesion at body temperature and easy removal at low temperature.
Atomic-layer-deposited alumina coatings (≈100 nm) with thermal-press sealing achieve IPX7 waterproofing.
Self-healing polymers repair cracks under 100 μm, extending lifespan by 30%.
Manufacturing includes two pathways:
Mass production: roll-to-roll processes integrating printing, coating, and cutting achieve thousands of units per hour.
Small-batch customization: DMD projection lithography + inkjet printing enables rapid prototyping.
